The present technology relates to a storage element and a memory which have a plurality of magnetic layers and perform recording while using a spin torque magnetization reversal.
Various types of information devices such as a mobile terminal and a mass storage server have made rapid progress. Therefore, memories and elements such as logic elements composing these devices have been expected to have higher performance such as high integration, high speed processing and low consumed power. Particularly, nonvolatile semiconductor memories have considerably made progress, and a flash memory acting as a mass storage file memory has been diffused so as to expel a hard disc drive. In contrast, a ferroelectric random access memory (FeRAM), a magnetic random access memory (MRAM), a phase-change random access memory (PCRAM) and the like have been developed so as to be used in place of a NOR flash memory, a dynamic random access memory (DRAM) and the like generally used now, while being considered to be used for a code storage and further to be developed as a working memory. A part of these developed RAMs have been already put to practical use.
The MRAM among these RAMs performs data recording based on the magnetization direction of a magnetic substance so as to be rewritable substantially limitless times (1015 times or more) at high speed. Therefore, the MRAM has been already used in fields of industrial automation, aircrafts and the like. Because of high speed operation and reliability of the MRAM, it is expected that the MRAM is developed as a code storage or a working memory. However, the MRAM has problems in actual use in view of low consumed power and large storage capacity. These problems result from a recording principle of the MRAM, that is, a recording method in which the magnetization direction is reversed by a magnetic field induced by an electric current of a wire.
As one of methods for solving these problems, recording not depending on the magnetic field of the current, that is, a magnetization reversing method has been examined. Especially, the spin torque magnetization reversal has been actively researched (e.g., refer to Patent Literatures (PTL) 1 and 2).
In the same manner as the MRAM, a storage element using the spin torque magnetization reversal is often structured by a magnetic tunnel junction (MTJ) and a tunneling magnetoresistive (TMR) element. In this structure, the phenomenon that a spin polarized electron passing through a magnetic layer of which magnetization is fixed in a direction gives a torque to another free magnetic layer (of which magnetization is not fixed) when entering this free magnetic layer (also called spin transfer torque) is utilized. When a current having a value equal to or more than a threshold value flows, the magnetization direction of this free magnetic layer is reversed. The rewriting of 0 and 1 is performed by changing the polarity of the current.
The absolute value of the current for the reversal of the magnetization is equal to or less than 1 mA when the storage element has the size of approximately 0.1 μm. Further, because this current value is decreased with the element volume, the size adjustment is possible. Moreover, because no word wire to induce the magnetic field of current for recording in the MRAM is used, there is a merit that the cell structure is simplified.
Hereinafter, the MRAM using the spin torque magnetization reversal is called a spin torque magnetic random access memory (ST-MRAM). The spin torque magnetization reversal is also called a spin injection magnetization reversal. This ST-MRAM is greatly expected as a nonvolatile memory in which low consumed power and large storage capacity are possible while the merits of the MRAM being operated at high speed and being rewritable substantially limitless times are maintained.